The problems of the viscous process led to the development of new processes for the manufacture of regenerated cellulose mouldings, in which the cellulose is brought into solution without chemical modification. The fibres and filaments obtained from these solutions are grouped under the designation “Lyocell”. Especially well-suited organic solvents are tertiary aminoxides, in particular N-methylmorpholin-N-oxide (NMMO). A process for the formation of a cellulose solution in aqueous NMMO is known from DE-A 44 41 468. The manufacture of cellulose mouldings from these solutions is described in EP-A 0 574 870.
In this solution the dissolved cellulose and the solvents, under the thermal conditions of a chemical decomposition, leads to discolourations of the spinning solution. Despite intensive washing of the cellulose mouldings formed, colouring substances remain in the mouldings, as a result of which the degree of whiteness is impaired. In order to reduce the decomposition referred to, a stabilizer is therefore added to the spinning solution. Suitable stabilizers are known from EP-A 0 047 929 and DD 218 104.
The principle is known from WO 97/23666 that the use of TCF-bleached cellulose pulp in the Lyocell process leads to mouldings with a higher degree of whiteness than the use of an ECF-bleached cellulose pulp. Both cellulose pulps are manufactured with similar high initial degrees of whiteness of about 90% and high degrees of purity, in particular with regard to the lignin content. It therefore seems questionable whether the TCF-cellulose pulp in general produces better degrees of whiteness of the cellulose mouldings manufactured from this cellulose pulp than an ECF-cellulose pulp.